The invention relates to a seal ring for sealing about a relatively-reciprocating and/or relatively-rotating machine part.
A known seal ring has a holding ring for fixedly mounting the seal ring on one machine part. An axially concentric guide ring is supported on one side on the holding ring and has a guiding surface on the other side for guiding the seal ring on another, relatively-movable machine part. At least one sealing ring of resiliently-deformable material engages the guide ring and has at least one sealing lip for engaging the relatively-movable part and sealing thereabout.
U.S Pat. No. 4,205,595 describes such a seal. It is for a double-acting piston in a pneumatic cylinder. Accordingly, it has two sealing rings and lips projecting in axially-opposite directions. An externally-open groove extending around the holding ring mounts the guide ring for engaging the inside wall of the pneumatic cylinder with its outermost, guiding surface. This construction provides stable association of the two sealing lips with the inside wall of the cylinder even when axially-uniform transverse forces normal to their axis are introduced between the piston and cylinder.
Conditions in this regard change fundamentally, however, if a tipping moment is introduced into the seal ring as can happen, for example, if the piston rod experiences a bending stress during its stroke. Such conditions are found in many operating piston/cylinder units, caused, for example, by the weight of the piston/cylinder unit itself. They are usually rectified but, if not, they result in less than optimum sealing characteristics and can lead to premature failure of the seal on account of the circumferentially-varying association of the sealing lips with the cylinder wall.